Composite materials are of great current interest because they provide a very favorable combination of high strength and low density. Typically, a composite material is comprised of fibers of graphite embedded within an epoxy, phenolic or other polymer resin matrix. The more advanced composites which have particularly favorable high strength to density ratio properties are especially attractive for aerospace applications. Typical of other advanced aerospace materials, they present comparative processing difficulties; it is insufficient to make a simple layup of the fibers and resin followed by room temperature curing. Aerospace composite materials not only involve more difficult to fabricate resins but often essentially defect-free finished parts must be produced.
Typically, composite components are cured using a flexing bagging material (e.g. silicone rubber sheet, nylon film) which is sealed to a tool (mold) and is in contact typically through a layer (e.g. peel ply, breather, bleeder) with the entire exposed surface area of the composite prepreg. The curing pressure is applied to the prepreg by direct contact of the bag. However, since the entire exposed prepreg surface must be in direct contact with the bag; design options are limited to simple shapes as it is difficult to reliably "bag" complex shapes. In addition, during cure, the laminate surface in contact with the bag under application of heat and pressure moves (e.g. creeps) as it debulks. This can result in the bag bridging (thereby not applying pressure to the area underneath the "bridge") or stretching to the point of rupture resulting in loss of the part. Finally, any tooling that is required for shape definition or location must be placed in direct contact with the laminate under the bag. This also limits designs to simple shapes that can be reliably bagged.
Accordingly, there has been a constant search in this field of art for new methods of making composite components.